1. Field of the Invention
This invention describes processes for preparing alpha-olefin polymers having particular viscosity characteristics and which are highly useful in drive train systems (gear, automatic transmission fluid, and the like) and hydraulic lubricant systems.
2. Introduction to the Invention
It is known that polymerized olefinic materials may be utilized as viscosity improving agents (commonly known as viscosity improvers) to prevent base oil stocks from thinning out at high temperatures or solidifying at low temperatures. If a base oil thins out at high temperatures then the essential lubricating characteristics of the composition can be lost. Thus, a viscosity improver is a material which at low temperatures retains fluidity (inhibits thickening or increasing viscosity) and at higher temperatures acts to maintain the viscosity of the entire fluid system as the temperature increases. It is highly desirable that a viscosity improver be shear stable. By being shear stable, it is meant that the viscosity improver under conditions of high shear does not degrade (undergo chain scission). If the viscosity improver is subject to high shear and chain scission, the effectiveness at high and low temperatures is reduced. The present invention deals with alpha-olefin polymers which are typically obtained from a binary catalyst system and which are highly shear stable.
Fontana et al U.S. Pat. No. 2,678,957 issued May 18, 1954 describes the polymerization of olefinic hydrocarbons. The catalyst system in the Fontana patent is described as AlBrX.sub.2 or AlBr.sub.2 X where X is a halogen other than bromine. The foregoing catalyst is stated as being dissolved in a non-polymerizable hydrocarbon solvent and in using a promoter. The promoter is RY where R is hydrogen or an alkyl group and Y is halogen. The monoalkylethylenes polymerized according to Fontana may be represented by the formula RCH.dbd.CH.sub.2 where R is an alkyl group. Fontana describes monomer materials ranging from propylene to octadecene-1.
Cesca et al U.S. Pat. No. 4,113,790 issued Sep. 12, 1988 teaches obtaining low molecular weight polymers by using an aluminum halide, and a halogen, metal halide or halogenated organic compound in a hydrocarbon solvent. Chen et al U.S. Pat. No. 4,558,170 issued Dec. 10, 1985 describes polyisobutylene production using an aluminum chloride-hydrogen chloride catalyst system.
Kramer U.S. Pat. No. 4,162,233 issued Jul. 24, 1979 describes a method for obtaining hydride transfer reaction products useful in isomerization and alkylation reactions. The stated acid systems utilized by Kramer are capable of stabilizing high concentrations of tertiary cations and further capable of forming carbonium ion salts including both dimeric and monomeric anions.
Hambling et al U.S. Pat. No. 3,436,379 issued Apr. 1, 1969 describes the copolymerization of monoolefinically unsaturated hydrocarbons, having a slower polymerization rate than isobutene, and one or more conjugated dienes in the presence of a Friedel-Crafts catalyst, and a minor proportion of isobutene. Furukawa et al U.S. Pat. No. 3,361,731 issued Jan. 2, 1968 describes the polymerization of vinyl ethers, styrene, alpha-methyl styrene and isobutylene with a catalyst system described as an aluminum halide etherate. Palmer U.S. Pat. No. 2,488,736 issued on Nov. 22, 1949 describes the polymerization of olefinic mixtures in the presence of a Friedel-Crafts catalyst of enhanced activity.
Hersberger U.S. Pat. No. 2,474,671 issued Jun. 28, 1949 describes a process for the Friedel-Crafts polymerization of unsaturated hydrocarbons to produce polymer products which are stated to be have uniform composition and physical properties regardless of the degree of polymerization.
Walsh et al U.S. Pat. No. 2,521,431 issued on Sep. 5, 1950 describes the polymerization of olefins. Walsh teaches that Friedel-Crafts catalysts may be utilized in the presence of an alkyl halide promoter for the polymerization reaction. Walsh states that the polymerization reaction may be improved by the addition of controlled amounts of water. Walsh et al U.S. Pat. No. 2,581,154 issued on Jan. 1, 1952. This Walsh patent describes the polymerization of low molecular weight unsaturated hydrocarbons in the presence of a Friedel-Crafts catalyst.
Calfee et al U.S. Pat. No. 2,644,798 issued Jul. 7, 1953 states that olefinic polymerization processes, and in particular those using aluminum halide catalysts, may be improved by using such catalysts having a molar ratio of halogen to metal of less than 3 and further containing oxygen in the catalyst molecules. The oxygenated aluminum halides are stated to be dissolved in a low-freezing, non-complex-forming solvent. The solvents include such materials as methyl chloride, ethyl chloride, or propyl chloride or other mono- or poly-halogenated alkanes containing up to about 5 carbon atoms.
Edwards U.S. Pat. No. 3,317,500 issued May 2, 1967 describes the production of hydrocarbon-insoluble elastomers obtained from 4-methyl-1-pentene. The polymerization of the subject olefin by Edwards is stated to take place in the presence of a catalyst which may be solid aluminum chloride or monoethyl aluminum chloride at temperatures at above -20.degree. F. (-29.degree. C.). Various methyl halide solvents are described as being useful by Edwards in his process. Edwards U.S. Pat. No. 3,317,501 issued May 2, 1967 contains similar disclosures.
It has been discovered in the present invention that shear stable liquid alpha-olefin polymers preferably being of a bimodal distribution may be obtained through the use of a catalyst system comprising a primary or secondary organo halide and a Lewis acid catalyst. The polymers are of low halide (halogen) content.
Throughout the specification and claims percentages and ratios are by weight, temperatures are in degrees Celsius and pressures are in KPa gauge unless otherwise indicated. Ranges and ratios given herein are exemplary and may be combined. To the extent that the references described herein are relevant, they are herein incorporated by reference.